1. Field of the Invention
The invention relates to Flight Management Systems (FMS) providing minimum total cost flight profiles particularly with respect to accounting for arrival error cost functions.
2. Description of the Prior Art
Flight Management Systems are known in the art that utilize an adjustable cost index in providing a minimum-cost flight profile. The ARINC characteristic 702 defines Flight Management Systems for commercial aircraft.
A principal objective of an FMS is to minimize the cost of flight. Present day equipment achieves this objective by generating vertical and lateral profiles that minimize direct operating cost (DOC). Direct operating cost is the cost of fuel plus other costs that are proportional to flight time. Flight time costs, such as crew costs, maintenance, repair and replacement of equipment, that may be prorated with flight time, is represented in the FMS by a cost index, which is defined as the ratio of time cost (dollars/hour) to fuel cost (cents/pound), providing units that are proportional to fuel flow (100 lb./hr). The cost index is selectable by the pilot (usually in the range of 0 to 999), and is intended to remain fixed for a given flight, representing predetermined flight-hour costs. For a given cost index, the prior art FMS provides a speed command at every point in the flight profile that minimizes DOC.
A significant disadvantage to the prior art FMS utilizing the DOC approach is that such systems do not reflect costs associated with arrival-time error, such as crew overtime, losses due to missed connections in connecting flights and potential losses resulting from customer dissatisfaction with the airline. The cost index is often utilized in prior art Flight Management Systems as a means for adjusting speed to achieve on-time arrival on an average basis. When utilized in this manner, the cost index for a city pair is selected to achieve the desired arrival time under average wind and traffic conditions. Therefore, in the prior art, the cost index is selected to achieve a statistical arrival time performance for a given city pair, without taking into account conditions for an individual flight. The cost index, when so utilized, no longer represents the flight-hour cost as initially intended, but becomes a mechanism for adjusting arrival time. It is appreciated that not arriving on time normally results in additional cost to a scheduled airline, which cost is not accounted for in present day flight management systems that search for the minimum cost profile in accordance with DOC.